Objective: To investigate the therapeutic effect of gene silencing peptidyl arginine deaminase 4 (PAD4) on pulmonary interstitial lesions induced by collagen-induced arthritis (CIA) mice, and possible mechanisms. Methods: A CIA mouse model was established in DBA/1 mice, followed by a tail vein injection of the virus solution prepared by the PAD4-siRNA expression vector once a week for 8 times. The mice were sacrificed at the end of the experiment. The expression of PAD4 mRNA in lungs was detected by real-time quantitative PCR (qRT-PCR). The expression of PAD4 protein was detected by tissue immunohistochemistry. Cell culture was performed by spleen tissue. Flow cytometry changes in the ratio of Tfh cells to Tfr cells were examined; lung staining was performed in the lungs to observe changes in lung pathology. Results: (1) Compared with the blank group, the expression of PAD4 mRNA in the lung tissue of the model group increased, the difference was statistically significant (P< 0.05). PAD4 mRNA in the lung tissue of the CIA mice after PAD4-siRNA treatment. The expression level was significantly lower than that of the model group and the negative control group, and the difference was statistically significant (P<0.05). (2) Red fluorescence was less in the lung tissue of the blank group, while more red fluorescence was observed in the inflammatory cell infiltration area and trachea around the lung tissue of the model group and the negative control group, and the red fluorescence of the three groups after PAD4-siRNA treatment was significantly reduced; (3) Compared with the blank group, the proportion of Tfh cells in the model group increased, the difference was statistically significant (P < 0.05), the proportion of Tfh cells in spleen cells of the CIA mice after PAD4-siRNA treatment was significantly lower than that of the model group and the negative control group, the difference was statistically significant (P < 0.05); compared with the blank group, in the mouse spleen cells in the model group the proportion of Tfr cells was slightly decreased, but the difference was not statistically signifi-cant. The proportion of Tfr cells in the spleen cells of the mice increased after PAD4-siRNA treatment, but the difference was statistically significant only in the PAD4-siRNA2 group compared with the model group and the negative control group (P<0.05); (4) The proportion of Tfh/Tfr in the spleen cells of the model group was increased, compared with the blank group, the difference was statistically significant (P<0.05); the ratio of Tfh/Tfr in the three groups after PAD4-siRNA treatment all decreased, the difference was statistically significant (P<0.05); (5) Compared with the blank group, the alveolar wall of the lung tissue of the model group was thickened, the inflammatory cell infiltration was increased, and the lung tissue destruction and inflammatory infiltration of the CIA mice were decreased after PAD4-siRNA treatment. The degree of reduction was reduced. Conclusion: Gene silencing of PAD4 can reduce the proportion of Tfh cells, increase the proportion of Tfr cells, reverse the proportion of Tfh/Tfr, and reduce the degree of interstitial lesions and inflammatory infiltration of lung tissue.